In multiple in-multiple out (MIMO) orthogonal frequency division multiplexing (OFDM) wireless communication systems, transmit beamforming (TxBF) typically will improve signal-to-noise ratio (SNR) at a receiver. Transmit beamforming may provide a higher throughput and in turn allow for higher data rates as compared to, for example, direct mapping or spatial spreading.
Channel state information (CSI) typically must be available at the transmitter in order to employ TxBF techniques. A transmitter may estimate CSI by assuming channel reciprocity, or the transmitter may determine CSI from a receiver by way of signaling. It should be noted that channel reciprocity requires radio calibration which could be achieved by exchanging sounding packets. The transmitter may then perform beamforming based on the estimation of received CSI and select a proper modulation and coding scheme (MCS) based on the MCS index recommended by the receiver through signaling.
Prior art wireless communication receivers utilize MCS indexes in order to match code rate and modulation as close as possible to channel conditions. However, since the number of MCS indexes is limited, MCS indexes selected by the receiver may not closely match the existing channel conditions. Prior art receivers select from a limited set of MCS indexes to match rate and modulations as closely as possible to channel conditions.
Therefore, it would be desirable to have a method and apparatus for redistributing power for all sub-carriers and eigenbeams within the set of selected MCS indexes. This would provide a fine adjustment to the MCS indexes in order to closely match current channel conditions.